The blaze reportedly erupted in Workshop No. 4, where containers of flammable substances were stored.
The initial cause of the fire appears to have been a gas cylinder explosion.
Footage published by the Telegram channel Shot claims to show the exact workshop where the blast took place, followed by a fire.
“Everybody out! Get out!” a man can be heard shouting in the background of one video.
Two welders were caught in the explosion’s epicenter and are in critical condition, according to Russian sources. Later updates indicated the number of injured had risen to three.
Russia’s Emergency Ministry in Karelia said the fire was burning inside an industrial unit, covering an area of about 1,500 square meters.
According to public records, the Onega shipyard was founded in 2002 in Petrozavodsk on the site of a former ship repair facility that belonged to the White Sea–Onega Shipping Company, which was established in 1944.